Electrolyte solutions for high energy cathode materials and methods for use

ABSTRACT

Described herein are materials for use in electrolytes that provide a number of desirable characteristics when implemented within batteries, such as high stability during battery cycling up to high temperatures, high voltages, high discharge capacity, high coulombic efficiency, and excellent retention of discharge capacity and coulombic efficiency over several cycles of charging and discharging. In some embodiments, a high voltage electrolyte includes a base electrolyte and a set of additive compounds, which impart these desirable performance characteristics.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.14/220,062 now U.S. Pat. No. 9,236,634, entitled “Electrolyte Solutionsfor High Energy Cathode Materials and Methods for Use” which was filedon Mar. 19, 2014, which is a continuation of International ApplicationNo. PCT/US2014/028304 entitled “Electrolyte Solutions For High EnergyCathode Materials And Methods For Use” which was filed on Mar. 14, 2014,which claims priority to U.S. Provisional Application No. 61/786,633entitled “Electrolyte Solutions For High Energy Cathode Materials AndMethods For Use” which was filed on Mar. 15, 2013. This applicationclaims priority to and the benefit of each of these applications, andeach application is incorporated herein by reference in its entirety.

BACKGROUND OF THE INVENTION

The present invention is in the field of battery technology and, moreparticularly, in the area of additive compounds for use with high energyelectrodes in electrochemical cells.

An electrolyte serves to transport ions and prevent electrical contactbetween electrodes in a battery. Organic carbonate-based electrolytesare most commonly used in lithium-ion (“Li-ion”) batteries and, morerecently, efforts have been made to develop new classes of electrolytesbased on sulfones, silanes, and nitriles. Unfortunately, theseconventional electrolytes typically cannot be operated at high voltages,since they are unstable above 4.3 V or other high voltages. At highvoltages, conventional electrolytes can decompose, for example, bycatalytic oxidation in the presence of cathode materials, to produceundesirable products that affect both the performance and safety of abattery. Conventional electrolytes may be degraded by reduction by theelectrodes when the cells are charged.

As described in more detail below, solvents, salts, or additives havebeen incorporated into the electrolyte to decompose to form a protectivefilm called a solid electrolyte interphase (SEI). Depending on the exactchemical system, this film can be composed of organic or inorganiclithium salts, organic molecules, oligomers, or polymers. Often, severalcomponents of the electrolyte are involved in the formation of the SEI(e.g. lithium salt, solvent, and additives). As a result, depending onthe rate of decomposition of the different components, the SEI can bemore or less homogenous.

In past research, organic compounds containing polymerizable functionalgroups such as alkenes, furan, thiophene, and pyrole had been reportedto form an SEI on the cathode of lithium ion batteries. See, e.g., Y.-S.Lee et al., Journal of Power Sources 196 (2011) 6997-7001. Theseadditives likely undergo polymerization during cell charging to formpassivation films on the electrodes. The improvement in cell performanceusing these materials was slight.

Further, certain organic polymers have also been used as bulkelectrolyte solvents for lithium ion batteries due to the generallysuperior chemical stability of polymeric-based solvents as compared tosmaller organic molecules, such as organic carbonates. However,practical application of such systems has been limited due to poor ionicconductivity.

For high energy cathode materials, electrolyte stability remains achallenge. Recently, the need for higher performance and high capacitylithium ion secondary batteries used for power sources is dramaticallyincreasing. Lithium transition metal oxides such as LiCoO₂ (“LCO”) andLiNi_(0.33)Mn_(0.33)CO_(0.33)O₂ (“NMC”) are state-of-the-art high energycathode materials used in commercial batteries. Yet only about 50% ofthe theoretical capacity of LCO or NMC cathodes can be used with stablecycle life. To obtain the higher capacity, batteries containing thesehigh energy materials need to be operated at higher voltages, such asvoltages up to about 4.7V. However, above about 4.3V, conventionalelectrolytes degrade and this leads to a significant deterioration ofthe cycle life. Further, the decomposition of the electrolyte at highervoltages can generate gas (such as CO₂, O₂, ethylene, H₂) and acidicproducts, both of which can damage a battery.

As disclosed herein, these challenges and others are addressed in highenergy lithium ion secondary batteries including cathode activematerials that are capable of operation at high voltages (at least about4.3V) with a carbon-based anode.

BRIEF SUMMARY OF THE INVENTION

Certain embodiments relate to a battery including an anode, a cathode,and an electrolyte including a lithium salt, a non-aqueous solvent, anda polymeric additive compound. The cathode material can be an NMCmaterial.

Certain embodiments include methods making, using, and conditioning suchbatteries for use.

Other aspects and embodiments of the invention are also contemplated.The foregoing summary and the following detailed description are notmeant to restrict the invention to any particular embodiment but aremerely meant to describe some embodiments of the invention.

BRIEF DESCRIPTION OF SEVERAL VIEWS OF THE DRAWINGS

FIG. 1 illustrates a Li-ion battery implemented in accordance with anembodiment of the invention.

FIG. 2 illustrates the operation of a Li-ion battery and a graphicalrepresentation of an illustrative non-limiting mechanism of action of anelectrolyte including an additive compound, according to an embodimentof the invention.

FIG. 3 illustrates characterization of the specific capacity versuscycle in NMC full cells using an activated carbon anode and electrolytesincluding an additive compound, according to an embodiment of theinvention, as compared to a control electrolyte.

FIG. 4 illustrates characterization of the capacity retention versuscycle in NMC full cells using an activated carbon anode and electrolytesincluding an additive compound, according to an embodiment of theinvention, as compared to a control electrolyte.

FIG. 5 illustrates characterization of the specific capacity versuscycle in NMC full cells using an activated carbon anode and electrolytesincluding an additive compound, according to an embodiment of theinvention, as compared to a control electrolyte.

FIG. 6 illustrates characterization of the capacity retention versuscycle in NMC full cells using an activated carbon anode and electrolytesincluding an additive compound, according to an embodiment of theinvention, as compared to a control electrolyte.

FIG. 7 illustrates characterization of the specific capacity versuscycle in NMC full cells using an activated carbon anode and electrolytesincluding an additive compound, according to an embodiment of theinvention, as compared to a control electrolyte.

FIG. 8 illustrates characterization of the capacity retention versuscycle in NMC full cells using an activated carbon anode and electrolytesincluding an additive compound, according to an embodiment of theinvention, as compared to a control electrolyte.

FIG. 9 illustrates characterization of the specific capacity versuscycle in NMC full cells using an activated carbon anode and electrolytesincluding an additive compound, according to an embodiment of theinvention, as compared to a control electrolyte and an electrolyte witha small molecule additive.

FIG. 10 illustrates characterization of the capacity retention versuscycle in NMC full cells using an activated carbon anode and electrolytesincluding an additive compound, according to an embodiment of theinvention, as compared to a control electrolyte and an electrolyte witha small molecule additive.

FIG. 11 illustrates characterization of the specific capacity versuscycle in NMC full cells using an activated carbon anode and electrolytesincluding an additive compound, according to an embodiment of theinvention, as compared to a control electrolyte and an electrolyte witha small molecule additive.

FIG. 12 illustrates characterization of the capacity retention versuscycle in NMC full cells using an activated carbon anode and electrolytesincluding an additive compound, according to an embodiment of theinvention, as compared to a control electrolyte and an electrolyte witha small molecule additive.

DETAILED DESCRIPTION OF THE INVENTION

The following definitions apply to some of the aspects described withrespect to some embodiments of the invention. These definitions maylikewise be expanded upon herein. Each term is further explained andexemplified throughout the description, figures, and examples. Anyinterpretation of the terms in this description should take into accountthe full description, figures, and examples presented herein.

The singular terms “a,” “an,” and “the” include the plural unless thecontext clearly dictates otherwise. Thus, for example, reference to anobject can include multiple objects unless the context clearly dictatesotherwise.

The terms “substantially” and “substantial” refer to a considerabledegree or extent. When used in conjunction with an event orcircumstance, the terms can refer to instances in which the event orcircumstance occurs precisely as well as instances in which the event orcircumstance occurs to a close approximation, such as accounting fortypical tolerance levels or variability of the embodiments describedherein.

The term “about” refers to the range of values approximately near thegiven value in order to account for typical tolerance levels,measurement precision, or other variability of the embodiments describedherein.

The term “specific capacity” refers to the amount (e.g., total ormaximum amount) of electrons or lithium ions a material is able to hold(or discharge) per unit mass and can be expressed in units of mAh/g. Incertain aspects and embodiments, specific capacity can be measured in aconstant current discharge (or charge) analysis, which includesdischarge (or charge) at a defined rate over a defined voltage rangeagainst a defined counterelectrode. For example, specific capacity canbe measured upon discharge at a rate of about 0.05 C (e.g., about 8.75mA/g) from 4.45 V to 3.0 V versus a Li/Li+ counterelectrode. Otherdischarge rates and other voltage ranges also can be used, such as arate of about 0.1 C (e.g., about 17.5 mA/g), or about 0.5 C (e.g., about87.5 mA/g), or about 1.0 C (e.g., about 175 mA/g).

A rate “C” refers to either (depending on context) the discharge currentas a fraction or multiple relative to a “1 C” current value under whicha battery (in a substantially fully charged state) would substantiallyfully discharge in one hour, or the charge current as a fraction ormultiple relative to a “1 C” current value under which the battery (in asubstantially fully discharged state) would substantially fully chargein one hour.

The term “rated charge voltage” refers to an upper end of a voltagerange during operation of a battery, such as a maximum voltage duringcharging, discharging, and/or cycling of the battery. In some aspectsand some embodiments, a rated charge voltage refers to a maximum voltageupon charging a battery from a substantially fully discharged statethrough its (maximum) specific capacity at an initial cycle, such as the1^(st) cycle, the 2^(nd) cycle, or the 3^(rd) cycle. In some aspects andsome embodiments, a rated charge voltage refers to a maximum voltageduring operation of a battery to substantially maintain one or more ofits performance characteristics, such as one or more of coulombicefficiency, retention of specific capacity, retention of energy density,and rate capability.

The term “rated cut-off voltage” refers to a lower end of a voltagerange during operation of a battery, such as a minimum voltage duringcharging, discharging, and/or cycling of the battery. In some aspectsand some embodiments, a rated cut-off voltage refers to a minimumvoltage upon discharging a battery from a substantially fully chargedstate through its (maximum) specific capacity at an initial cycle, suchas the 1^(st) cycle, the 2^(nd) cycle, or the 3^(rd) cycle, and, in suchaspects and embodiments, a rated cut-off voltage also can be referred toas a rated discharge voltage. In some aspects and some embodiments, arated cut-off voltage refers to a minimum voltage during operation of abattery to substantially maintain one or more of its performancecharacteristics, such as one or more of coulombic efficiency, retentionof specific capacity, retention of energy density, and rate capability.

The “maximum voltage” refers to the voltage at which both the anode andthe cathode are fully charged. In an electrochemical cell, eachelectrode may have a given specific capacity and one of the electrodeswill be the limiting electrode such that one electrode will be fullycharged and the other will be as fully charged as it can be for thatspecific pairing of electrodes. The process of matching the specificcapacities of the electrodes to achieve the desired capacity of theelectrochemical cell is “capacity matching.”

The term “LCO” refers generally to cathode materials containingLiCo_(x)O_(y) and includes, but is not limited to, cathode materialscontaining LiCoO₂.

The term “NMC” refers generally to cathode materials containingLiNi_(x)Mn_(y)Co_(z)O_(w) and includes, but is not limited to, cathodematerials containing LiNi_(0.33)Mn_(0.33)Co_(0.33)O₂.

To the extent certain battery characteristics can vary with temperature,such characteristics are specified at room temperature (about 30 degreesC.), unless the context clearly dictates otherwise.

Ranges presented herein are inclusive of their endpoints. Thus, forexample, the range 1 to 3 includes the values 1 and 3 as well asintermediate values.

FIG. 1 illustrates a Li-ion battery 100 implemented in accordance withan embodiment of the invention. The battery 100 includes an anode 102, acathode 106, and a separator 108 that is disposed between the anode 102and the cathode 106. In the illustrated embodiment, the battery 100 alsoincludes a high voltage electrolyte 104, which is disposed between theanode 102 and the cathode 106 and remains stable during high voltagebattery cycling.

The operation of the battery 100 is based upon reversible intercalationand de-intercalation of Li ions into and from host materials of theanode 102 and the cathode 106. Other implementations of the battery 100are contemplated, such as those based on conversion chemistry. Referringto FIG. 1, the voltage of the battery 100 is based on redox potentialsof the anode 102 and the cathode 106, where Li ions are accommodated orreleased at a lower potential in the former and a higher potential inthe latter. To allow both a higher energy density and a higher voltageplatform to deliver that energy, the cathode 106 includes an activecathode material for high voltage operations at or above 4.3 V.

Examples of suitable high voltage cathode materials include phosphates,fluorophosphates, fluorosulphates, fluorosilicates, spinels, Li-richlayered oxides, and composite layered oxides. Further examples ofsuitable cathode materials include: spinel structure lithium metaloxides, layered structure lithium metal oxides, lithium-rich layeredstructured lithium metal oxides, lithium metal silicates, lithium metalphosphates, metal fluorides, metal oxides, sulfur, and metal sulfides.Examples of suitable anode materials include conventional anodematerials used in Li-ion batteries, such as lithium, graphite(“Li_(x)C₆”), and other carbon, silicate, or oxide-based anodematerials.

FIG. 2 illustrates operation of a Li-ion battery and an illustrative,non-limiting mechanism of action of an improved electrolyte, accordingto an embodiment of the invention. Without being bound by a particulartheory not recited in the claims, the inclusion of one or morestabilizing additive compounds in an electrolyte solution can, uponoperation of the battery (e.g., during conditioning thereof), passivatea high voltage cathode material, thereby reducing or preventingreactions between bulk electrolyte components and the cathode materialthat can degrade battery performance.

Referring to FIG. 2, an electrolyte 202 includes a base electrolyte,and, during initial battery cycling, components within the baseelectrolyte can assist in the in-situ formation of a protective film (inthe form of a solid electrolyte interface (“SEI”) 206) on or next to ananode 204. The anode SEI 206 can inhibit reductive decomposition of thehigh voltage electrolyte 202. Preferably, and without being bound bytheory not recited in the claims, for operation at voltages at or above4.2 V, the electrolyte 202 can also include additives that can assist inthe in-situ formation of a protective film (in the form of a SEI 208 oranother derivative) on or next to a cathode 200. The cathode SEI 208 caninhibit oxidative decomposition of the high voltage electrolyte 202 thatcan otherwise occur during high voltage operations. As such, the cathodeSEI 208 can inhibit oxidative reactions in a counterpart manner to theinhibition of reductive reactions by the anode SEI 206. In theillustrated embodiment, the cathode SEI 208 can have a thickness in thesub-micron range, and can include one or more chemical elementscorresponding to, or derived from, those present in one or moreadditives, such as silicon or other heteroatom included in one or moreadditives. Advantageously, one or more additives can preferentiallypassivate the cathode 200 and can selectively contribute towards filmformation on the cathode 200, rather than the anode 204. Suchpreferential or selective film formation on the cathode 200 can impartstability against oxidative decomposition, with little or no additionalfilm formation on the anode 204 (beyond the anode SEI 206) that canotherwise degrade battery performance through resistive losses. Moregenerally, one or more additives can decompose below a redox potentialof the cathode material and above a redox potential of SEI formation onthe anode 204.

Without being bound by a particular theory not recited in the claims,the formation of the cathode SEI 208 can occur through one or more ofthe following mechanisms: (1) the additive compound(s) can decompose toform the cathode SEI 208, which inhibits further oxidative decompositionof electrolyte components; (2) the additive compound(s) or itsdecomposed product(s) form or improve the quality of a passivation filmon the cathode or anode; (3) the additive compounds can form anintermediate product, such as a complex with LiPF₆ or a cathodematerial, which intermediate product then decomposes to form the cathodeSEI 208 that inhibits further oxidative decomposition of electrolytecomponents; (4) the additive compounds can form an intermediate product,such as a complex with LiPF₆, which then decomposes during initialcharging. The resulting decomposition product can then further decomposeduring initial charging to form the cathode SEI 208, which inhibitsfurther oxidative decomposition of electrolyte components; (5) theadditive compounds can stabilize the cathode material by preventingmetal ion dissolution.

Other mechanisms of action of the electrolyte 202 are contemplated,according to an embodiment of the invention. For example, and in placeof, or in combination with, forming or improving the quality of thecathode SEI 208, one or more additives or a derivative thereof (e.g.,their decomposition product) can form or improve the quality of theanode SEI 206, such as to reduce the resistance for Li ion diffusionthrough the anode SEI 206. As another example, one or more additives ora derivative thereof (e.g., their decomposition product) can improve thestability of the electrolyte 202 by chemically reacting or forming acomplex with other electrolyte components. As a further example, one ormore additives or a derivative thereof (e.g., their decompositionproduct) can scavenge decomposition products of other electrolytecomponents or dissolved electrode materials in the electrolyte 202 bychemical reaction or complex formation. Any one or more of the cathodeSEI 208, the anode SEI 206, and the other decomposition products orcomplexes can be viewed as derivatives, which can include one or morechemical elements corresponding to, or derived from, those present inone or more additives, such as a heteroatom included in the additives.

Certain embodiments are related to a class of polymeric additives fornon-aqueous electrolytes. Such embodiments include several electrolyteadditives that improve the oxidative stability of the electrolyte andthe cycle life and coulombic efficiency of electrochemical cellscontaining these additives.

A high voltage electrolyte according to some embodiments of theinvention can be formed with reference to the formula:base electrolyte+additive compound(s)→high voltage electrolyte   (1)

A high temperature electrolyte according to some embodiments of theinvention can be formed with reference to the formula:base electrolyte+additive compound(s)→high temperature electrolyte   (2)

In formulas (1) and (2), the base electrolyte can include a set ofsolvents and a set of salts, such as a set of Li-containing salts in thecase of Li-ion batteries. Examples of suitable solvents includenonaqueous electrolyte solvents for use in Li-ion batteries, includingcarbonates, such as ethylene carbonate, dimethyl carbonate, ethyl methylcarbonate, propylene carbonate, methyl propyl carbonate, and diethylcarbonate; sulfones; silanes; nitriles; esters; ethers; and combinationsthereof.

Referring to formulas (1) and (2), an amount of a particular compoundcan be expressed in terms of a weight percent of the compound relativeto a total weight of the electrolyte solution (or wt. %). For example,an amount of a compound can be in the range of about 0.01 wt. % to about30 wt. %, such as from about 0.05 wt. % to about 30 wt. %, from about0.01 wt. % to about 20 wt. %, from about 0.2 wt. % to about 15 wt. %,from about 0.2 wt. % to about 10 wt. %, from about 0.2 wt. % to about 5wt. %, or from about 0.2 wt. % to about 1 wt. %, and, in the case of acombination of multiple compounds, a total amount of the compounds canbe in the range of about 0.01 wt. % to about 30 wt. %, such as fromabout 0.05 wt. % to about 30 wt. %, from about 0.01 wt. % to about 20wt. %, from about 0.2 wt. % to about 15 wt. %, from about 0.2 wt. % toabout 10 wt. %, from about 0.2 wt. % to about 5 wt. %, or from about 0.2wt. % to about 1 wt. %. An amount of a compound also can be expressed interms of a ratio of the number of moles of the compound per unit surfacearea of either, or both, electrode materials. For example, an amount ofa compound can be in the range of about 10⁻⁷ mol/m²to about 10⁻² mol/m²,such as from about 10⁻⁷ mol/m²to about 10⁻⁵ mol/m², from about 10⁻⁵mol/m² to about 10⁻³ mol/m², from about 10⁻⁶ mol/m² to about 10⁻⁴mol/m², or from about 10⁻⁴ mol/m² to about 10⁻² mol/m². As furtherdescribed below, a compound can be consumed or can react, decompose, orundergo other modifications during initial battery cycling. As such, anamount of a compound can refer to an initial amount of the compound usedduring the formation of the electrolyte solutions according to formulas(1) or (2), or can refer to an initial amount of the additive within theelectrolyte solution prior to battery cycling (or prior to anysignificant amount of battery cycling).

Resulting performance characteristics of a battery can depend upon theidentity of a particular compound used to form the high voltageelectrolyte according to formulas (1) or (2), an amount of the compoundused, and, in the case of a combination of multiple compounds, arelative amount of each compound within the combination. Accordingly,the resulting performance characteristics can be fine-tuned or optimizedby proper selection of the compounds and adjusting amounts of thecompounds in formulas (1) or (2).

The formation according to formulas (1) or (2) can be carried out usinga variety of techniques, such as by mixing the base electrolyte and theadditives, dispersing the additives within the base electrolyte,dissolving the additives within the base electrolyte, or otherwiseplacing these components in contact with one another. The additives canbe provided in a liquid form, a powdered form (or another solid form),or a combination thereof. The additives can be incorporated in theelectrolyte solutions of formulas (1) or (2) prior to, during, orsubsequent to battery assembly.

The electrolyte solutions described herein can be used for a variety ofbatteries containing a high voltage cathode or a low voltage cathode,and in batteries operated at high temperatures. For example, theelectrolyte solutions can be substituted in place of, or used inconjunction with, conventional electrolytes for Li-ion batteries foroperations at or above 4.3 V. In particular, these additives are usefulfor Li-ion batteries containing LCO or NMC cathode materials.

Batteries including the electrolyte solutions can be conditioned bycycling prior to commercial sale or use in commerce. Such conditioningcan include, for example, providing a battery, and cycling such batterythrough at least 1, at least 2, at least 3, at least 4, or at least 5cycles, each cycle including charging the battery and discharging thebattery at a rate of 0.05 C (e.g., a current of 8.75 mA/g) between 4.45V and 3.0 V (or another voltage range) versus a referencecounterelectrode, such as a graphite anode. Charging and discharging canbe carried out at a higher or lower rate, such as at a rate of 0.1 C(e.g., a current of 17.5 mA/g), at a rate of 0.5 C (e.g., a current of87.5 mA/g), or at a rate of 10 (e.g., a current of 175 mA/g). Typicallya battery is conditioned with 1 cycle by charging at 0.05 C rate to 4.45V followed by applying constant voltage until the current reaches 0.02C, and then discharging at 0.05 C rate to 3V.

The polymer-based additives according to embodiments herein aremolecules formed from numerous repeated monomer units, as isconventionally understood in the art. Such polymer-based additives maycontain various functional groups attached to the polymer chain. Certainproperties are preferred in polymer-based additives for use inbatteries. For example, the additives preferably are: (i) soluble in theelectrolyte solvent (that is, they are sufficiently polar as compared tothe solvent and sufficiently low molecular weight); (ii) eitherchemically resistant to oxidation and/or reduction under the cellconditions or, if not chemically resistant to oxidation and/orreduction, then the additives should decompose to intermediates orproducts that form a stable SEI film on the anode, cathode, or both; and(iii) sufficiently low molecular weight to be soluble in electrolytesolution at room temperature and to make the electrolyte solutionviscosity not worse than without the additive.

Certain polymer-based additives demonstrate the properties listed above,including: poly(9-vinylcarbazole); poly(methyl vinyl ether-alt-maleicanhydride); poly(oxy-1,4-phenylenesulfonyl-1,4-phenylene);poly(1-hexadecene-sulfone); poly(hexafluoropropylene oxide);poly(bis(4-(ethoxycarbonyl)phenoxy)phosphazene); and combinationsthereof.

These polymer additives are soluble in the conventional electrolyte andhave functional groups that contribute to stable SEI formation. Thesepolymer additives can form more mechanically and chemically stable SEIfilms compared with molecular or short-chain oligomers. These polymeradditives significantly improve cycle life in a full cell configuration.Importantly, these polymer additives show superior performance whencompared to their monomer analogues, which indicates that incorporationof the functional groups into a polymer background is responsible forthe improved performance. That is, the functional groups alone, in anon-polymeric structure, do not deliver the levels of performanceachieved using their polymeric equivalents.

Several tests were conducted on full cells constructed according to themethods described below. The battery cell was cycled between 3 V to 4.45V, or in some cases to about 4.65V, at 30° C. Capacity, coulombicefficiency, discharge rate performance, and cycle life were evaluated.From these tests the following performance improvements were observed:

TABLE 1 Summary of performance of polymer additives Discharge CapacityCoulombic Rate Cycle Polymer (mAh/g, Efficiency Performance lifeAdditives cy1) (%, cy1) (1 C/0.1 C, %) (%, cy99) 0.5% PVC 168 78 98 852% PMVEAMA 171 80 95 83 2% POPSP 169 79 95 86 0.5% PHDS 175 79 94 83 2%PHFPO 175 80 94 81 Control 174 78 94 72

FIG. 3 illustrates characterization of the specific capacity versuscycle in NMC full cells using an activated carbon anode. The control isa commercial carbonate electrolyte (empty circle). All three additivesdemonstrate superior performance as compared to the commercialelectrolyte. 0.5 wt % poly(1-hexadecene-sulfone) added to commercialelectrolyte (solid triangle), 0.5 wt % poly(9-vinylcarbazole) added tocommercial electrolyte (cross), and or 2 wt % poly(hexafluoropropyleneoxide) added to commercial electrolyte (empty triangle) all demonstratehigher capacity at high cycles numbers than the control.

FIG. 4 illustrates characterization of the capacity retention versuscycle in NMC full cells using an activated carbon anode. The control isa commercial carbonate electrolyte (empty circle). All three additivesdemonstrate superior performance as compared to the commercialelectrolyte. 0.5 wt % poly(1-hexadecene-sulfone) added to commercialelectrolyte (solid triangle), 0.5 wt % poly(9-vinylcarbazole) added tocommercial electrolyte (cross), and or 2 wt % poly(hexafluoropropyleneoxide) added to commercial electrolyte (empty triangle) all demonstratehigher capacity at high cycles numbers than the control.

FIG. 5 illustrates characterization of the specific capacity versuscycle in NMC full cells using an activated carbon anode. The control isa commercial carbonate electrolyte (empty circle). Poly(methyl vinylether-alt-maleic anhydride) demonstrates superior performance ascompared to the commercial electrolyte at both 0.5 wt % added tocommercial electrolyte (solid square) and 2 wt % added to commercialelectrolyte (solid cross).

FIG. 6 illustrates characterization of the capacity retention versuscycle in NMC full cells using an activated carbon anode. The control isa commercial carbonate electrolyte (empty circle). Poly(methyl vinylether-alt-maleic anhydride) demonstrates superior performance ascompared to the commercial electrolyte at both 0.5 wt % added tocommercial electrolyte (solid square) and 2 wt % added to commercialelectrolyte (solid cross).

FIG. 7 illustrates characterization of the specific capacity versuscycle in NMC full cells using an activated carbon anode. The control isa commercial carbonate electrolyte (empty circle).Poly(oxy-1,4-phenylenesulfonyl-1,4-phenylene) demonstrates superiorperformance as compared to the commercial electrolyte at both 0.5 wt %added to commercial electrolyte (empty square) and 2 wt % added tocommercial electrolyte (solid star).

FIG. 8 illustrates characterization of the capacity retention versuscycle in NMC full cells using an activated carbon anode. The control isa commercial carbonate electrolyte (empty circle).Poly(oxy-1,4-phenylenesulfonyl-1,4-phenylene) demonstrates superiorperformance as compared to the commercial electrolyte at both 0.5 wt %added to commercial electrolyte (empty square) and 2 wt % added tocommercial electrolyte (solid star).

To test whether the observed performance improvements were due to thespecific functional groups without the polymer backbone or if theimprovements were due to the polymer-based structure of the additives,poly(9-vinylcarbazole) and poly(oxy-1,4-phenylenesulfonyl-1,4-phenylene)were tested versus their monomeric analogues: 9-ethylcarbazole,9-vinylcarbazole, and 4-methoxyphenyl phenyl sulfone.

FIG. 9 illustrates characterization of the specific capacity versuscycle in NMC full cells using an activated carbon anode. The polymeradditives 0.5 wt % poly(9-vinylcarbazole) added to commercialelectrolyte (solid circle) showed superior cycle life to 0.5 wt %9-vinylcarbazole added to commercial electrolyte (cross).9-vinylcarbazole is monomeric precursor of poly(9-vinylcarbazole). Thepolymer additives 0.5 wt % poly(9-vinylcarbazole) added to commercialelectrolyte (solid circle) also showed superior cycle life to 0.5 wt %9-ethylcarbazole added to commercial electrolyte (empty triangle)although two additives share the same functional group 9-ethylcarbazole.

FIG. 10 illustrates characterization of the capacity retention versuscycle in NMC full cells using an activated carbon anode. The polymeradditives 0.5 wt % poly(9-vinylcarbazole) added to commercialelectrolyte (solid circle) showed superior cycle life to 0.5 wt %9-vinylcarbazole added to commercial electrolyte (cross). The polymeradditives 0.5 wt % poly(9-vinylcarbazole) added to commercialelectrolyte (solid circle) also showed superior cycle life to 0.5 wt %9-ethylcarbazole added to commercial electrolyte (empty triangle).

These results indicate that presence of the polymeric backbone in theseadditives is important to the improved cycle performance. Notably, itwas theorized that 9-vinylcarbazole would undergo polymerizationreaction to form polycarbazole under electrochemical condition. Thisresult indicates that preexisting polymeric chain of polymer additivescan further improve the cycle life, possibly by forming a more robustand homogenous SEI. Thus, we demonstrated that polymer precursors do notimprove performance like the preexisting polymer.

FIG. 11 illustrates characterization of the specific capacity versuscycle in NMC full cells using an activated carbon anode. The polymeradditives 0.5 wt % poly(oxy-1,4-phenylenesulfonyl-1,4-phenylene) addedto commercial electrolyte (solid circle) showed superior cycle life to0.5 wt % 4-methoxyphenyl phenyl sulfone added to commercial electrolyte(empty triangle). 4-methoxyphenyl phenyl sulfone is monomeric precursorof poly(oxy-1,4-phenylenesulfonyl-1,4-phenylene).

FIG. 12 illustrates characterization of the capacity retention versuscycle in NMC full cells using an activated carbon anode. The polymeradditives 0.5 wt % poly(oxy-1,4-phenylenesulfonyl-1,4-phenylene) addedto commercial electrolyte (solid circle) showed superior cycle life to0.5 wt % 4-methoxyphenyl phenyl sulfone added to commercial electrolyte(empty triangle).

In addressing the challenges of high energy cathode materials, theadditives according to embodiments disclosed herein have a number ofbenefits, including: (i) large surface area, which allows the polymericadditives to strongly adsorb on to the surface of the electrodes beforedecomposition and potentially improving the quality and stability of theresulting SEI; (ii) mechanical and chemical stability as compared toorganic oligomers and short-chain polymers formed from conventionalsolvents and additives due to the pre-formed polymer backbone; and (iii)homogenous dispersal of functional groups throughout the SEI film due tothose functional groups being distributed along a polymeric backbone.

Further, additives according to embodiments described herein providedsuperior performance as compared to their related monomers or relatedsmall molecules with lesser molar concentration of additives. In thecomparative experiments herein, the polymers and the monomers werecompared at the same weight percentage, but the monomer was 100%functional group while some of the polymeric additive was polymerbackbone and not functional group. Thus, less functional group providedbetter performance in the polymer-based additives.

In some embodiments, the additive is a polymer having at least onefunctional group selected from the group consisting of carbazoles,anhydrides, sulfones, fluorinated ethers, phosphazenes, esters, andcombinations thereof.

The following examples describe specific aspects of some embodiments ofthe invention to illustrate and provide a description for those ofordinary skill in the art. The examples should not be construed aslimiting the invention, as the examples merely provide specificmethodology useful in understanding and practicing some embodiments ofthe invention.

EXAMPLES

Battery cells were formed in a high purity Argon filled glove box(M-Braun, O₂ and humidity content <0.1 ppm). The electrodes wereprepared by the following methods. (i) For the cathode, a commercialLiNi_(0.33)Mn_(0.33)Co_(0.33)O₂ cathode material was mixed withpoly(vinylidene fluoride) (Sigma Aldrich) and carbon black (Super P Li,TIMCAL) with 1-methyl-2-pyrrolidinone (Sigma Aldrich) as solvent. Theresulting slurry was deposited on an aluminum current collector anddried to form a composite cathode film. (ii) For the anode, a graphiticcarbon (G5) was mixed with poly(vinylidene fluoride) (Sigma Aldrich) andcarbon black (Super P Li, TIMCAL) with 1-methyl-2-pyrrolidinone (SigmaAldrich) as solvent. The resulting slurry was deposited on a coppercurrent collector and dried to form a composite cathode film. Eachbattery cell included the composite cathode film, a polypropyleneseparator, and the composite anode film. A conventional electrolyte wasmixed with a given electrolyte additive and added to the battery cell.The battery cell was sealed and cycled between 3 V to 4.45 V, or even at4.65V, at 30 degrees C.

While the invention has been described with reference to the specificembodiments thereof, it should be understood by those skilled in the artthat various changes may be made and equivalents may be substitutedwithout departing from the true spirit and scope of the invention asdefined by the appended claims. In addition, many modifications may bemade to adapt a particular situation, material, composition of matter,method, or process to the objective, spirit and scope of the invention.All such modifications are intended to be within the scope of the claimsappended hereto. In particular, while the methods disclosed herein havebeen described with reference to particular operations performed in aparticular order, it will be understood that these operations may becombined, sub-divided, or re-ordered to form an equivalent methodwithout departing from the teachings of the invention. Accordingly,unless specifically indicated herein, the order and grouping of theoperations are not limitations of the invention.

What is claimed is:
 1. A battery capable of several cycles of chargingand discharging comprising: an anode; a cathode; and a liquidelectrolyte comprising a lithium salt, a non-aqueous solvent, and apolymeric additive, wherein the polymeric additive includespoly(bis(4-(ethoxycarbonyl)phenoxy)phosphazene and is soluble in thenon-aqueous solvent at 30° C.
 2. The battery of claim 1 wherein aconcentration of the polymeric additive is no less than 0.2 weightpercent and no greater than 10 weight percent of a total weight of theliquid electrolyte.
 3. The battery of claim 1 wherein the battery ischaracterized by a rated charge voltage greater than about 4.2 V.
 4. Thebattery of claim 1 wherein the battery is characterized by a ratedcharge voltage greater than about 4.5 V.
 5. The battery of claim 1wherein the battery is characterized by a rated charge voltage greaterthan about 4.7 V.
 6. The battery of claim 1 wherein the battery ischaracterized by a rated charge voltage greater than about 4.9 V.
 7. Thebattery of claim 1 wherein the cathode comprises nickel, manganese, andcobalt.
 8. The battery of claim 1 wherein the anode comprises activatedcarbon.
 9. A method of making a high voltage battery capable of severalcycles of charging and discharging, comprising: providing a liquidelectrolyte solution comprising a lithium salt, a non-aqueous solvent,and a polymeric additive, wherein the polymeric additive includespoly(methyl vinyl ether-alt-maleic anhydride) and is soluble in thenon-aqueous solvent at 30° C.; providing an anode; providing a cathode;assembling the anode and cathode and a separator into an electrochemicalcell; adding the liquid electrolyte solution to the cell; and sealingthe cell to form the high voltage battery.
 10. The method of claim 9wherein the cathode comprises nickel, manganese, and cobalt.
 11. Themethod of claim 9 wherein the anode comprises activated carbon.
 12. Thebattery of claim 1, wherein the polymeric additive does not increase theviscosity of the liquid electrolyte.
 13. A battery capable of severalcycles of charging and discharging comprising: an anode; a cathode; anda liquid electrolyte comprising a lithium salt, a non-aqueous solvent,and a polymeric additive, wherein the polymeric additive includespoly(methyl vinyl ether-alt-maleic anhydride) and is soluble in thenon-aqueous solvent at 30° C.
 14. The battery of claim 13, wherein aconcentration of the polymeric additive is no less than 0.2 weightpercent and no greater than 10 weight percent of a total weight of theliquid electrolyte.
 15. The battery of claim 13, wherein the battery ischaracterized by a rated charge voltage greater than about 4.2 V. 16.The battery of claim 13, wherein the battery is characterized by a ratedcharge voltage greater than about 4.5 V.
 17. The battery of claim 13,wherein the battery is characterized by a rated charge voltage greaterthan about 4.7 V.
 18. The battery of claim 13, wherein the battery ischaracterized by a rated charge voltage greater than about 4.9 V. 19.The battery of claim 13, wherein the cathode comprises nickel,manganese, and cobalt.
 20. The battery of claim 13, wherein the anodecomprises activated carbon.